Java SE: Bitwise and Bit Shift Operations

1. Java provides operators to perform bitwise and bit shift operations on int type.

    The operators discussed in the section are less commonly used, the intent is to simply make you aware that these operators exist.

 

2.  Bitwise operators overview:

Operator Name Example Result Description

a & b	and	3 & 5	1	1 if both bits are 1.
a | b	or	3 | 5	7	1 if either bit is 1.
a ^ b	xor	3 ^ 5	6	1 if both bits are different.
~a	not	~3	-4	Inverts the bits.
n << p	left shift	3 <<< 2	12	Shifts the bits of n left p positions. Zero bits are shifted into the low-order positions.
n >> p	right shift	5 >> 2	1	Shifts the bits of n right p positions. If n is a 2's complement signed number, the sign bit is shifted into the high-order positions.
n >>> p	right shift	-4 >>> 28	15	Shifts the bits of n right p positions. Zeros are shifted into the high-order positions.

 

3. Examples

    1) "AND" example:

    @Test
    public void andTest() {
	int i = 12;
	// i = 0000,0000,0000,0000,0000,0000,0000,1100
	int j = -3;
	// -3 = ~2 -> ~0000,0000,0000,0000,0000,0000,0000,0010 -> 1111,1111,1111,1111,1111,1111,1111,1101
	int k = i & j;
	// 0000,0000,0000,0000,0000,0000,0000,1100 & 
	// 1111,1111,1111,1111,1111,1111,1111,1101 ->
	// 0000,0000,0000,0000,0000,0000,0000,1100 ->12
	assertEquals(12, k);
    }

    2) "OR" example:

    @Test
    public void orTest() {
	int i = 12;
	// i = 0000,0000,0000,0000,0000,0000,0000,1100
	int j = -32768;
	// -32768 = ~32767 -> ~0000,0000,0000,0000,0111,1111,1111,1111 ->
	// 1111,1111,1111,1111,1000,0000,0000,0000
	int k = i | j;
	// 0000,0000,0000,0000,0000,0000,0000,1100 |
	// 1111,1111,1111,1111,1000,0000,0000,0000 ->
	// 1111,1111,1111,1111,1000,0000,0000,1100 ->
	// -(~1111,1111,1111,1111,1000,0000,0000,1100 + 1) ->
	// -( 0000,0000,0000,0000,0111,1111,1111,0100) -> -32756
	assertEquals(-32756, k);
    }

    3) "XOR" example:

    @Test
    public void xorTest() {
	int i = 32756;
	// i = 0000,0000,0000,0000,0111,1111,1111,0100
	int j = -32768;
	// -32768 = ~32767 -> ~0000,0000,0000,0000,0111,1111,1111,1111 ->
	// 1111,1111,1111,1111,1000,0000,0000,0000
	int k = i ^ j;
	// 0000,0000,0000,0000,0111,1111,1111,0100 ^
	// 1111,1111,1111,1111,1000,0000,0000,0000 ->
	// 1111,1111,1111,1111,1111,1111,1111,0100 ->
	// -(~1111,1111,1111,1111,1111,1111,1111,0100 + 1) ->
	// -( 0000,0000,0000,0000,0000,0000,0000,1100) -> -12
	assertEquals(-12, k);
    }

    4) "NOT" test

    @Test
    public void notTest() {
	int i = -12;
	// ~11 ->
	// ~0000,0000,0000,0000,0000,0000,0000,1011 ->
	// 1111,1111,1111,1111,1111,1111,1111,0100
	int j = ~i;
	// ~1111,1111,1111,1111,1111,1111,1111,0100
	// 0000,0000,0000,0000,0000,0000,0000,1011
	assertEquals(11, j);

	i = -32768;
	j = ~i;
	assertEquals(32767, j);

	i = 0XFFFFFFFF;
	j = ~i;
	assertEquals(0, j);
    }

    5) "Left Shift" test:

    @Test
    public void leftShiftTest() {
	int i = 12;
	// 0000,0000,0000,0000,0000,0000,0000,1100
	int j = i << 1;
	// 0000,0000,0000,0000,0000,0000,0001,1000
	assertEquals(24, j);
	
	i = 0X8000000F;
	// 1000,0000,0000,0000,0000,0000,0000,1111
	j = i << 1;
	// 0000,0000,0000,0000,0000,0000,0001,1110
	assertEquals(30, j);
    }

    6) "Right Shift" test:

    @Test
    public void rightShiftTest() {
	int i, j;
	i = 12;
	// 0000,0000,0000,0000,0000,0000,0000,1100
	j = i >> 1;
	// 0000,0000,0000,0000,0000,0000,0000,0110
	assertEquals(6, j);
	j = i >>> 1;
	// 0000,0000,0000,0000,0000,0000,0000,0110
	assertEquals(6, j);
	
	i = 0X8000000F;
	// 1000,0000,0000,0000,0000,0000,0000,1111
	j = i >> 1;
	// 1100,0000,0000,0000,0000,0000,0000,0111
	assertEquals(0XC0000007, j);
	j = i >>> 1;
	// 0100,0000,0000,0000,0000,0000,0000,0111
	assertEquals(0X40000007, j);
    }

 

4. P.S

    1) The size of "int" in java is 32-bit that is 8-byte, thus we can represent that with 8 hex number.

    2) The left most bit represents the sign, 0 for positive and 1 for negative.

    3) There is no unsigned int/byte data type in java, and we can use "long" if needed.

 

 

Reference Links:

1) http://docs.oracle.com/javase/tutorial/java/nutsandbolts/op3.html

2) http://www.leepoint.net/notes-java/data/expressions/bitops.html

3) http://stackoverflow.com/questions/9854166/declaring-an-unsigned-int-in-java